Autothermal process for the production of olefins

ABSTRACT

A process and catalyst for the partial oxidation of paraffinic hydrocarbons, such as ethane, propane, naphtha, and natural gas condensates, to olefins, such as ethylene and propylene. The process involves contacting a paraffinic hydrocarbon with oxygen in the presence of a catalyst under autothermal process conditions. The catalyst comprises a Group 8B metal and, optionally, a promoter metal, such as tin or copper, supported on a fiber monolith support, preferably a ceramic fiber mat monolith. In another aspect, the invention is a process of oxidizing a paraffinic hydrocarbon to an olefin under autothermal conditions in the presence of a catalyst comprising a Group 8B metal and, optionally, a promoter metal, the metals being loaded onto the front face of a monolith support. An on-line method of synthesizing and regenerating catalysts for autothermal oxidation processes is also disclosed. This divisional case covers the catalyst composition and the method of preparing an olefin using the catalyst.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. application Ser. No.09/388,218, filed Sep. 1, 1999 and U.S. Provisional Application Ser. No.60/099,042, filed Sep. 3, 1998.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to the field of catalytic oxidationof hydrocarbons. More particularly, the present invention relates to thecatalytic partial oxidation of paraffinic hydrocarbons, such as ethane,propane, and naphtha, to produce olefins, such as ethylene andpropylene.

[0003] Olefins find widespread utility in industrial organic chemistry.Ethylene is needed for the preparation of important polymers, such aspolyethylene, vinyl plastics, and ethylene-propylene rubbers, andimportant basic chemicals, such as ethylene oxide, styrene,acetaldehyde, ethyl acetate, and dichloroethane. Propylene is needed forthe preparation of polypropylene plastics, ethylene-propylene rubbers,and important basic chemicals, such as propylene oxide, cumene, andacrolein. Isobutylene is needed for the preparation of methyl tertiarybutyl ether. Long chain mono-olefins find utility in the manufacture oflinear alkylated benzene sulfonates, which are used in the detergentindustry.

[0004] Low molecular weight olefins, such as ethylene, propylene, andbutylene, are produced almost exclusively by thermal cracking(pyrolysis/steam cracking) of alkanes at elevated temperatures. Anethylene plant, for example, typically achieves an ethylene selectivityof about 85 percent calculated on a carbon atom basis at an ethaneconversion of about 60 mole percent. Undesired coproducts are recycledto the shell side of the cracking furnace to be burned, so as to producethe heat necessary for the process. Disadvantageously, thermal crackingprocesses for olefin production are highly endothermic. Accordingly,these processes require the construction and maintenance of large,capital intensive, and complex cracking furnaces. The heat required tooperate these furnaces at a temperature of about 900° C. is frequentlyobtained from the combustion of methane which disadvantageously producesundesirable quantities of carbon dioxide and nitrogen oxides. As afurther disadvantage, the crackers must be shut down periodically toremove coke deposits on the inside of the cracking coils.

[0005] Catalytic processes are known wherein paraffinic hydrocarbons areoxidatively dehydrogenated to form mono-olefins. In these processes, aparaffinic hydrocarbon is contacted with oxygen in the presence of acatalyst consisting of a platinum group metal or mixture thereofdeposited on a ceramic monolith support in the form of a honeycomb.Optionally, hydrogen may be a component of the feed. The catalyst,prepared using conventional techniques, is uniformly loaded throughoutthe support. The process can be conducted under autothermal reactionconditions wherein a portion of the feed is combusted, and the heatproduced during combustion drives the oxidative dehydrogenation process.Consequently, under autothermal process conditions there is no externalheat source required. Representative references disclosing this type ofprocess include the following U.S. Pat. Nos. 4,940,826; 5,105,052; and5,382,741. A similar process is taught, for example, in U.S. Pat. No.5,625,111, wherein the ceramic monolith support is in the form of afoam, rather than a honeycomb. Disadvantageously, substantial amounts ofdeep oxidation products, such as carbon monoxide and carbon dioxide, areproduced, and the selectivity to olefins remains too low when comparedwith thermal cracking. As a further disadvantage, with prolonged use athigh temperatures, the ceramic honeycomb and foam monoliths are subjectto catastrophic fracture.

[0006] C. Yokoyama, S. S. Bharadwaj and L. D. Schmidt disclose inCatalysis Letters, 38, 1996, 181-188, the oxidative dehydrogenation ofethane to ethylene under autothermal reaction conditions in the presenceof a bimetallic catalyst comprising platinum and a second metal selectedfrom tin, copper, silver, magnesium, cerium, lanthanum, nickel, cobalt,and gold supported on a ceramic foam monolith. The use of a catalystcomprising platinum with tin and/or copper results in an improved olefinselectivity; however, the ceramic foam monolith is still prone tocatastrophic fracture.

[0007] In view of the above, it would be desirable to discover acatalytic process wherein a paraffinic hydrocarbon is converted to anolefin in a conversion and selectivity comparable to commercial thermalcracking processes. It would be desirable if the catalytic process wereto produce small quantities of deep oxidation products, such as carbonmonoxide and carbon dioxide. It would also be desirable if the processwere to achieve low levels of catalyst coking. It would be even moredesirable if the process could be easily engineered without thenecessity for a large, capital intensive, and complex cracking furnace.Finally, it would be most desirable if the catalyst was stable and thecatalytic support not prone to fracture.

SUMMARY OF THE INVENTION

[0008] In one aspect, this invention is a process for the partialoxidation of a paraffinic hydrocarbon to form an olefin. The processcomprises contacting a paraffinic hydrocarbon with oxygen in thepresence of a catalyst. The contacting is conducted under autothermalprocess conditions sufficient to form the olefin. The catalyst employedin the process of this invention comprises at least one Group 8B metalsupported on a fiber monolith support. Optionally, the catalyst mayadditionally comprise at least one promoter metal.

[0009] The process of this invention efficiently produces olefins,particularly mono-olefins, from paraffinic hydrocarbons and oxygen. Inpreferred embodiments, the process of this invention achieves a higherparaffin conversion and a higher olefin selectivity as compared withprior art catalytic, autothermal processes. Accordingly, in preferredembodiments, the process of this invention produces fewer undesirabledeep oxidation products, such as carbon monoxide and carbon dioxide, ascompared with prior art catalytic, autothermal processes. Even moreadvantageously, in preferred embodiments, the process of this inventionachieves a paraffin conversion and olefin selectivity which arecomparable to commercial thermal cracking processes. As a furtheradvantage, the process produces little, if any, coke, therebysubstantially eliminating problems with coking. Most advantageously, theprocess of this invention allows the operator to employ a simpleengineering design and eliminates the requirement for a large,expensive, and complex furnace, as in thermal cracking processes. Morespecifically, since the residence time of the reactants in the processof this invention is on the order of milliseconds, the reaction zoneused in this process operates at high volumetric throughput.Accordingly, the reaction zone measures from about one-fiftieth to aboutone-hundredth the size of a commercially available steam cracker ofcomparable capacity. The reduced size of the reactor reduces costs andgreatly simplifies catalyst loading and maintenance procedures. Finally,since the process of this invention is exothermic, the heat produced canbe harvested via integrated heat exchangers to produce energy, forexample, in the form of steam credits, for other processes.

[0010] In another aspect, this invention is a catalyst compositioncomprising at least one Group 8B metal and at least one promoter metal,said metals being supported on a fiber monolith support.

[0011] The aforementioned composition is beneficially employed as acatalyst in the autothermal partial oxidation of a paraffinichydrocarbon to an olefin. In preferred embodiments, the catalystcomposition beneficially produces the olefin at conversions andselectivities which are comparable to those of industrial thermalcracking processes. As another advantage, the catalyst composition ofthis invention exhibits good catalyst stability. Additionally, the fibermonolith support which is used in the composition of this invention canbe advantageously manufactured into a variety of configurations, suchas, without limitation, planar, tubular, and undulating configurations,for specific beneficial results, such as, to maximize the contactingconditions of the reactants with the catalyst and to minimize thepressure drop across the catalyst. As a further advantage, whendeactivated the catalyst is easily removed from the reactor andreplaced. Most advantageously, the fiber monolith support which is usedin the catalyst of this invention is not prone to fracture as are theprior art honeycomb and foam monoliths.

[0012] In yet another aspect, this invention is a method of synthesizingor regenerating a catalyst on-line in an autothermal process ofoxidizing a paraffinic hydrocarbon to an olefin. For the purposes ofthis aspect of the invention, the catalyst comprises a Group 8B metaland, optionally, a promoter metal on a monolith support. The term“on-line” means the monolith support, either blank or in the form of afully deactivated or partially deactivated catalyst, is loaded in thereactor and operating under ignition or autothermal process conditions.A “blank” support is a fresh support absent any Group 8B and, optional,promoter metals. The synthesis/regeneration method comprises contactingthe front face of a monolith support with a Group 8B metal compoundand/or a promoter metal compound, the contacting being conducted in situunder ignition conditions or autothermal process conditions.

[0013] The aforementioned method beneficially allows for the synthesisof an oxidation catalyst on-line under ignition conditions.Additionally, the aforementioned method beneficially allows for theregeneration of a deactivated or partially deactivated oxidationcatalyst on-line under autothermal conditions. The method of thisinvention eliminates the necessity of preparing the catalyst prior toloading a reactor and eliminates the necessity of shutting down thereactor to regenerate or replace the deactivated catalyst. As a furtheraspect of this invention, novel catalyst compositions can be preparedand screened on-line for catalytic activity. The regeneration processcan be beneficially employed on-line to replace metal components of thecatalyst which are lost over time through vaporization. Dead sections ofthe catalyst can be reactivated or regenerated on-line. Theaforementioned advantages simplify the handling and maintenance of thecatalyst, reduce costs, and improve process efficiency.

[0014] The aforementioned on-line method of preparing or regeneratingcatalysts for autothermal processes produces catalysts in which theactive catalytic components are selectively deposited on the front faceof the monolith support. Thus, in another aspect, this invention is acatalyst composition comprising at least one Group 8B metal and,optionally, at least one promoter metal, said metal(s) being supportedon the front face of a monolith support.

[0015] The catalyst composition, described hereinabove, is characterizedby front face loading of the Group 8B element(s) and promoter element(s)onto the monolith support. This catalyst can be employed in the partialoxidation of a paraffinic hydrocarbon to an olefin under autothermalprocess conditions. Catalysts which are front face loaded advantageouslyexhibit improved activity in these oxidation processes, as compared withcatalysts characterized by uniform loading throughout the support.

[0016] In yet another aspect, this invention is a second process ofpartially oxidizing a paraffinic hydrocarbon to an olefin. The processcomprises contacting a paraffinic hydrocarbon with oxygen in thepresence of a catalyst under autothermal process conditions. Thecatalyst used herein comprises at least one Group 8B metal and,optionally, at least one promoter metal, said metal(s) being loaded ontothe front face of a monolith support.

[0017] The aforementioned second autothermal oxidation process employs acatalyst characterized by front face loading of the Group 8B element(s)and optional promoter element(s) onto a monolith support. This secondautothermal oxidation process enjoys all of the benefits of the firstautothermal oxidation process employing fiber monolith supports,described hereinbefore. More advantageously, the process of thisinvention characterized by front face loading of the catalyst results ina higher paraffin conversion and a higher olefin selectivity, ascompared with catalysts having uniform loading throughout the support.

BRIEF DESCRIPTION OF THE DRAWING

[0018]FIG. 1 is an illustration of a reactor which can be used tosynthesize or regenerate oxidation catalysts on-line under hightemperature conditions, such as the ignition or autothermal conditionsof the oxidation process of this invention.

DETAILED DESCRIPTION OF THE INVENTION

[0019] The oxidation process of this invention involves the partialoxidation of a paraffinic hydrocarbon to form an olefin. The words“partial oxidation” imply that the paraffin is not substantiallyoxidized to deep oxidation products, specifically, carbon monoxide andcarbon dioxide. Rather, the partial oxidation comprises one or both ofoxidative dehydrogenation and cracking to form primarily olefins. It isnot known or suggested to what extent or degree either reaction,oxidative dehydrogenation or cracking, predominates or occurs to theexclusion of the other. The process comprises contacting a paraffinichydrocarbon with oxygen in the presence of a catalyst. The contacting isconducted under autothermal process conditions sufficient to form theolefin. In one aspect, the catalyst which is employed in the process ofthis invention comprises at least one Group 8B metal and, optionally, atleast one promoter metal, said metal(s) being supported on a fibermonolith support. In another aspect, the catalyst employed in theprocess of this invention comprises at least one Group 8B metal and,optionally, at least one promoter metal, said metal(s) being loaded ontothe front face of a monolith support. The term “monolith” refers to acontinuous structure, as described in detail hereinafter.

[0020] In a preferred embodiment of this invention, the paraffin isselected from ethane, propane, mixtures of ethane and propane, naphtha,gas oils, vacuum gas oils, natural gas condensates, and mixtures of theaforementioned hydrocarbons; and the preferred olefins produced areethylene, propylene, butene, isobutylene, and butadiene.

[0021] In another preferred aspect, the Group 8B metal is a platinumgroup metal. In a more preferred aspect, the platinum group metal isplatinum. The preferred promoter metal is selected from the elements ofGroups 2A, 1B, 3A, 4A, (equivalent to Groups 2, 11, 13, 14), and thelanthanide rare earth metals of the Periodic Table of the Elements, asreferenced by S. R. Radel and M. H. Navidi, in Chemistry, WestPublishing Company, New York, 1990. Mixtures of the aforementionedpromoter metals can also be employed.

[0022] Any paraffinic hydrocarbon or mixture of paraffinic hydrocarbonscan be employed in the process of this invention provided that anolefin, preferably, a mono-olefin, is produced. The term “paraffinichydrocarbon,” as used herein, refers to a saturated hydrocarbon.Generally, the paraffinic hydrocarbon contains at least 2 carbon atoms.Preferably, the paraffinic hydrocarbon contains from 2 to about 25carbon atoms, preferably, from 2 to about 15 carbon atoms, and even morepreferably, from 2 to about 10 carbon atoms. The paraffinic hydrocarboncan have a linear, cyclic, or branched structure, and can be a liquid orgas at ambient temperature and pressure. The paraffinic hydrocarbon canbe supplied as an essentially pure paraffinic compound or as aparaffin-containing mixture of hydrocarbons. Paraffinic hydrocarbonfeeds which are suitably employed in the process of this inventioninclude, but are not limited to, ethane, propane, butane, pentane,hexane, heptane, octane, isomers and higher homologues thereof, as wellas complex higher boiling mixtures of paraffin-containing hydrocarbons,such as naphtha, gas oils, vacuum gas oils, and natural gas condensates.Additional feed components may include methane, nitrogen, carbonmonoxide, carbon dioxide, and steam, if so desired. Minor amounts ofunsaturated hydrocarbons may also be present. Most preferably, theparaffinic hydrocarbon is selected from ethane, propane, mixtures ofethane and propane, naphtha, natural gas condensates, and mixtures ofthe aforementioned hydrocarbons.

[0023] In the process of this invention, the paraffinic hydrocarbon iscontacted with an oxygen-containing gas. Preferably, the gas ismolecular oxygen or molecular oxygen diluted with an unreactive gas,such as nitrogen, helium, or argon. Any molar ratio of paraffinichydrocarbon to oxygen is suitable provided the desired olefin isproduced in the process of this invention. Preferably, the process isconducted fuel-rich and above the upper flammability limit. A fuel-richfeed reduces the selectivities to deep oxidation products, such ascarbon monoxide and carbon dioxide, and beneficially increases theselectivity to olefins. Above the upper flammability limit, homogeneous(gas phase) combustion of the feed is not self-sustaining; therefore,the feed is safer to handle. One skilled in the art would know how todetermine the upper flammability limit for different feedstream mixturescomprising the paraffinic hydrocarbon, oxygen, and optionally, hydrogenand a diluent.

[0024] Generally, the molar ratio of hydrocarbon to oxygen variesdepending upon the specific paraffin feed and process conditionsemployed. Typically, the molar ratio of paraffinic hydrocarbon to oxygenranges from about 3 to about 77 times the stoichiometric ratio ofhydrocarbon to oxygen for complete combustion to carbon dioxide andwater. Preferably, the molar ratio of paraffinic hydrocarbon to oxygenranges from about 3 to about 13, more preferably, from about 4 to about11, and most preferably, from about 5 to about 9 times thestoichiometric ratio of hydrocarbon to oxygen for complete combustion tocarbon dioxide and water. These general limits are usually achieved byemploying a molar ratio of paraffinic hydrocarbon to oxygen greater thanabout 0.1:1, preferably, greater than about 0.2:1, and by using a molarratio of paraffinic hydrocarbon to oxygen usually less than about 3.0:1,preferably, less than about 2.7:1. For preferred paraffinichydrocarbons, the following ratios are more specific. For ethane, theethane to oxygen molar ratio is typically greater than about 1.5:1, andpreferably, greater than about 1.8:1. The ethane to oxygen molar ratiois typically less than about 3.0:1, preferably, less than about 2.7:1.For propane, the propane to oxygen molar ratio is typically greater thanabout 0.9:1, preferably, greater than about 1.1:1. The propane to oxygenmolar ratio is typically less than about 2.2:1, preferably, less thanabout 2.0:1. For naphtha, the naphtha to oxygen molar ratio is typicallygreater than about 0.3:1, preferably, greater than about 0.5:1. Thenaphtha to oxygen molar ratio is typically less than about 1.0:1,preferably, less than about 0.9:1.

[0025] Optionally, hydrogen may be co-fed with the paraffinichydrocarbon and oxygen to the catalyst. The presence of hydrogen in thefeedstream beneficially improves the conversion of the paraffinichydrocarbon and the selectivity to olefins, while reducing the formationof deep oxidation products, such as, carbon monoxide and carbon dioxide.The molar ratio of hydrogen to oxygen can vary over any operable rangeprovided that the desired olefin product is produced. Typically, themolar ratio of hydrogen to oxygen is greater than about 0.5:1,preferably, greater than about 0.7:1, and more preferably, greater thanabout 1.5:1. Typically, the molar ratio of hydrogen to oxygen is lessthan about 3.2:1, preferably, less than about 3.0:1, and morepreferably, less than about 2.7:1.

[0026] Optionally, the feed may contain a diluent, which can be any gasor vaporizable liquid which is substantially unreactive in the processof the invention. The diluent functions as a carrier of the reactantsand products and facilitates the transfer of heat generated by theprocess. The diluent also helps to minimize undesirable secondaryreactions and helps to expand the non-flammable regime for mixtures ofthe paraffinic hydrocarbon and oxygen, and optionally hydrogen. Suitablediluents include nitrogen, argon, helium, carbon dioxide, steam, andmethane. The concentration of diluent in the feed can vary over a widerange. If used, the concentration of diluent is typically greater thanabout 0.1 mole percent of the total reactant feed including paraffinichydrocarbon, oxygen, diluent, and optional hydrogen. Preferably, theamount of diluent is greater than about 1 mole percent of the totalreactant feed. Typically, the amount of diluent is less than about 70mole percent, and preferably, less than about 40 mole percent, of thetotal reactant feed.

[0027] In one aspect, the catalyst which is employed in the process ofthis invention beneficially comprises at least one Group 8B metal, andoptionally, at least one promoter metal supported on a fiber monolithsupport. The Group 8B metals comprise iron, cobalt, nickel, and theplatinum group metals, including ruthenium, rhodium, palladium, osmium,iridium, and platinum. Mixtures of the aforementioned Group 8B metalsmay also be used. Preferably, the Group 8B metal is a platinum groupmetal; more preferably, the platinum group metal is platinum. Thecatalyst optionally comprises at least one promoter metal, which issuitably defined as any metal which is capable of enhancing the activityof the catalyst, as measured, for example, by an increase in theparaffinic hydrocarbon conversion, an increase in the selectivity toolefin, a decrease in the formation of deep oxidation products, such ascarbon monoxide and carbon dioxide, and/or an increase in catalyststability and lifetime. Typically, the term “promoter metal” does notinclude the Group 8B metals. Preferably, the promoter metal is selectedfrom the elements of Groups 2A (for example, Mg, Ca, Sr, Ba), 1B (Cu,Ag, Au), 3A (for example, Al, Ga, In), 4A (for example, Ge, Sn, Pb), thelanthanide rare earth metals, and mixtures thereof. More preferably, thepromoter metal is selected from copper, tin and mixtures thereof.

[0028] If a promoter metal is employed, then any atomic ratio of Group8B metal to promoter metal is suitable, provided the catalyst isoperable in the process of this invention. The optimal atomic ratio willvary with the specific Group 8B and promoter metals employed. Generally,the atomic ratio of the Group 8B metal to promoter metal is greater thanabout 0.1 (1:10), preferably, greater than about 0.13 (1:8), and morepreferably, greater than about 0.17 (1:6). Generally, the atomic ratioof the Group 8B metal to promoter metal is less than about 2.0 (1:0.5),preferably, less than about 0.33 (1:3), and more preferably, less thanabout 0.25 (1:4). Compositions prepared with promoter metal alone, inthe absence of Group 8B metal, are typically (but not always)catalytically inactive in the process. In contrast, the Group 8B metalis catalytically active in the absence of promoter metal, albeit withlesser activity.

[0029] The loading of the Group 8B metal on the fiber support can be anywhich provides for an operable catalyst in the process of thisinvention. In general, the loading of the Group 8B metal can be as lowas about 0.0001 weight percent, based on the total weight of the Group8B metal and support. Preferably, the loading of the Group 8B metal isless than about 80 weight percent, preferably, less than about 60 weightpercent, and more preferably, less than about 10 weight percent, basedon the total weight of the Group 8B metal and the support. Once theplatinum loading is established, the desired atomic ratio of Group 8Bmetal to promoter metal determines the loading of the promoter metal.

[0030] In one aspect of this invention, the catalytic support is a fibermonolith. As used herein, the term “monolith” means any continuousstructure, preferably, in one piece or unit. As an example, a pluralityof fibers can be woven into a cloth or made into non-woven mats or thinpaper-like sheets to form a fiber monolith. In another example, one longcontinuous fiber can be wound upon itself and used as a fiber monolith.Catalysts prepared with fiber monoliths tend to have a higher activityas compared with catalysts prepared with foam monoliths and gauzes.Additionally, fibers possess higher fracture resistance as compared withfoam and honeycomb supports of the prior art.

[0031] Preferably, the catalytic support is a ceramic fiber monolith.Non-limiting examples of ceramics which are suitable for this inventioninclude refractory oxides and carbides, such as, alumina, silica,silica-aluminas, aluminosilicates, including cordierite, zirconia,titania, boria, zirconia mullite alumina (ZTA), lithium aluminumsilicates, and oxide-bonded silicon carbide. Mixtures of theaforementioned refractory oxides and carbides may also be employed.Preferred ceramics include alumina, silica, and amorphous or crystallinecombinations of alumina and silica, including mullite. Alpha (α) andgamma (γ) alumina are preferred. Preferred combinations of alumina andsilica comprise from about 60 to about 100 weight percent alumina andfrom essentially zero to about 40 weight percent silica. Otherrefractory oxides, such as boria, can be present in smaller amounts inthe preferred alumina and silica mixtures. Preferred zirconias includezirconia fully stabilized with calcia (SSZ) and zirconia partiallystabilized with magnesia (PSZ).

[0032] More preferred ceramic fibers, such as those available as Nextel®brand ceramic fibers (a trademark of 3M Corporation), typically have adiameter greater than about 1 micron (μm), preferably, greater thanabout 5 microns (μm). The diameter is suitably less than about 20 μm,preferably, less than about 15 μm. The length of the fibers is generallygreater than about 0.5 inch (1.25 cm), preferably, greater than about 1inch (2.5 cm), and typically less than about 10 inches (25.0 cm),preferably, less than about 5 inches (12.5 cm). The surface area of thefibers is very low, being generally less than about 1 m²/g, preferably,less than about 0.3 m²/g, but greater than about 0.001 m²/g. Preferably,the fibers are not woven like cloth, but instead are randomlyintertwined as in a non-woven mat or matted rug. Most preferred areNextel® brand 312 fibers which consist essentially of alumina (62 weightpercent), silica (24 weight percent), and boria (14 weight percent).Non-limiting examples of other suitable fibers include Nextel® brand 440fibers which consist essentially of gamma alumina (70 weight percent),silica (28 weight percent), and boria (2 weight percent) and Nexte®brand 610 fibers which consist essentially of alpha alumina (99 weightpercent), silica (0.2-0.3 weight percent) and iron oxide (0.4-0.7 weightpercent). Preferably, the fibers are not wash-coated.

[0033] The deposition of the Group 8B metal and promoter metal onto thesupport can be made by any technique known to those skilled in the art,for example, impregnation, ion-exchange, deposition-precipitation, vapordeposition, sputtering, and ion implantation. In one preferred methodthe Group 8B metal is deposited onto the support by impregnation.Impregnation is described by Charles N. Satterfield in HeterogeneousCatalysis in Practice, McGraw-Hill Book Company, New York, 1980, 82-84,incorporated herein by reference. In this procedure, the support iswetted with a solution containing a soluble Group 8B metal compound,preferably, to the point of incipient wetness. The temperature of thedeposition typically ranges from about ambient, taken as 23° C., toabout 100° C., preferably, from about 23° C. to about 50° C. Thedeposition is conducted usually at ambient pressure. Non-limitingexamples of suitable Group 8B metal compounds include the Group 8B metalnitrates, halides, sulfates, alkoxides, carboxylates, and Group 8B metalorganometallic compounds, such as halo, amino, and carbonyl complexes.Preferably, the Group 8B metal compound is a platinum group halide, morepreferably, a chloride, such as chloroplatinic acid. The solvent can beany liquid which solubilizes the Group 8B metal compound. Suitablesolvents include water, aliphatic alcohols, aliphatic and aromatichydrocarbons, and halo-substituted aliphatic and aromatic hydrocarbons.The concentration of the Group 8B metal compound in the solutiongenerally ranges from about 0.001 molar (M) to about 10 M. Aftercontacting the support with the solution containing the Group 8B metalcompound, the support may be dried under air at a temperature rangingfrom about 23° C. to a temperature below the decomposition temperatureof the Group 8B metal compound, typically, a temperature between about23° C. and about 100° C.

[0034] The deposition of the promoter metal can be accomplished in amanner analogous to the deposition of the Group 8B metal. Accordingly,if impregnation is used, then the support is wetted with a solutioncontaining a soluble promoter metal compound at a temperature betweenabout 23° C. and about 100° C., preferably, between about 23° C. andabout 50° C., at about ambient pressure. Suitable examples of solublepromoter metal compounds include promoter metal halides, nitrates,alkoxides, carboxylates, sulfates, and promoter metal organometalliccompounds, such as amino, halo, and carbonyl complexes. Suitablesolvents comprise water, aliphatic alcohols, aliphatic and aromatichydrocarbons, and chloro-substituted aliphatic and aromatichydrocarbons. Certain promoter metal compounds, such as compounds oftin, may be more readily solubilized in the presence of acid, such ashydrochloric acid. The concentration of the promoter metal compound inthe solution generally ranges from about 0.01 M to about 10 M. Followingdeposition of the soluble promoter metal compound or mixture thereof,the impregnated support may be dried under air at a temperature betweenabout 23° C. and a temperature below the temperature whereinvaporization or decomposition of the promoter metal compound occurs.Typically, the drying is conducted at a temperature between about 23° C.and about 100° C.

[0035] In one method of preparing the catalyst, the Group 8B metal isdeposited onto the support first, and thereafter the promoter metal isdeposited onto the support. In an alternative method, the promoter metalis deposited first, followed by the deposition of the Group 8B metal. Ina preferred method of preparing the catalyst, the Group 8B metal and thepromoter metal are deposited simultaneously onto the support from thesame deposition solution.

[0036] Following one or more depositions of the Group 8B metal andoptional promoter metal onto the support, a calcination under oxygen isoptional. If performed, the calcination is conducted at a temperatureranging from about 100° C. to below the temperature at whichvolatilization of the metals becomes significant, typically, atemperature less than about 1,100° C. Preferably, the calcination isconducted at a temperature between 100° C. and about 500° C.

[0037] As a final step in the preparation of the catalyst, the fullyloaded support is reduced under a reducing agent, such as hydrogen,carbon monoxide, or ammonia, at a temperature between about 100° C. andabout 800° C., preferably between about 125° C. and about 600° C., so asto convert the Group 8B metal substantially to its elemental form. Thepromoter metal may be reduced fully or partially, or not reduced at all,depending upon the specific promoter metal chosen and the reductionconditions. In addition, reduction at elevated temperatures may producealloys of the Group 8B metal and the promoter metal. Alloys may provideenhanced catalyst stability by retarding vaporization of the promotermetal during the process of this invention.

[0038] In another preferred embodiment, the Group 8B metal(s) andoptional promoter metal(s) are loaded onto the front face, that is, theupstream face, of the monolith support, as opposed to being uniformlyloaded throughout the support. Front face (or up-front) loading leads toimproved selectivity to olefins in the oxidation process of thisinvention. As a guideline, the term “front face loading” may beinterpreted to mean that typically greater than about 65 weight percent,preferably, greater than about 75 weight percent, and more preferably,greater than about 90 weight percent, of the Group 8B metal and optionalpromoter metal(s), are supported within the front ⅓ of the thickness ofthe support. Preferably, these amounts of metals are supported withinthe front 3 mm of the support. If the support is not yet loaded into thereactor, front face loading can be accomplished by conventionaltechniques, such as, impregnation onto the front face of a blank supportwith solutions of the platinum and promoter metals. In a more preferredembodiment, the front face-loaded catalyst is prepared on-line, that is,prepared after the support, typically a blank support, is loaded intothe reactor, placed under reaction conditions, and contacted with aGroup 8B metal compound and, optionally, a promoter metal compound.On-line front face loading facilitates the synthesis and screening ofnew catalysts without shutting down and reloading the reactor.Regeneration of the catalyst can also be conducted on-line, as notedhereinafter. Advantageously, the on-line front face loading methoddescribed herein is generally adaptable to other high temperaturecatalytic processes.

[0039] As noted hereinabove, on-line up-front loading can beaccomplished by contacting the front face of the monolith support,typically a blank monolith, with at least one Group 8B metal compoundand/or at least one promoter metal compound, the contacting beingconducted in situ, that is, in the reactor under process conditions. Forthis aspect of the invention, the monolith can take any form, including,a foam or honeycomb, a fiber mat, a gauze, or any other regular orirregular, continuous particle or structure. For this aspect of theinvention, the term “process conditions” includes ignition andautothermal conditions, described in detail hereinafter. Typically,ignition conditions are used when a catalyst is being synthesized from ablank monolith. Typically, autothermal conditions are used when apartially deactivated catalyst is being regenerated. The contacting canbe continuous or intermittent, as desired. A preferred method ofcontacting comprises dripping or spraying a solution containing asoluble compound of the Group 8B metal and/or promoter metal onto thefront face of the support. The solution containing the metal componentscan be, for example, any of the impregnation solutions used in thecatalyst preparation described hereinbefore.

[0040] In one preferred embodiment, the reactor for achieving on-linesynthesis and regeneration comprises the design shown in FIG. 1. In thisdesign, the blank monolith or the catalyst itself (1) is packed into aquartz reactor (2). A radiation shield (not shown in figure) ispreferably placed below the monolith or catalyst. A port (3) above thefront face of the monolith or catalyst provides an entry for thefeedstream containing the paraffinic hydrocarbon, oxygen, and optionaldiluent and hydrogen. The feedstream passes through the catalyst to thedownstream exit port (not shown). Above the front face of the monolithor catalyst a second port (4) provides a means for introducing the Group8B metal compound and/or promoter metal compound into the reactor.Suitable means, as shown in FIG. 1, can be a hypodermic syringe (5) witha needle (6) passing through a rubber septum (7) into the reactor (2).Other suitable delivery means include pipets, spray nozzles, faucets,and other conventional devices designed for the delivery of solutionsinto high temperature reactors. The entire reactor (2) can be wrapped inhigh temperature insulation (not shown in the figure) so as to retardheat losses and maintain adiabatic or near adiabatic conditions.

[0041] The process of this invention is required to be conducted underautothermal process conditions. Under these conditions, the heatgenerated by the combustion of a portion of the feed is sufficient tosupport the dehydrogenation and/or thermal cracking of the paraffin tothe olefin. Accordingly, the need for an external heat source to supplythe energy for the process is eliminated. As a requirement forconducting an autothermal process, the catalyst should be capable ofcombustion beyond the normal fuel rich limit of flammability. Thecatalyst of this invention possesses this required capability. Ignitioncan be effected by preheating the feed to a temperature sufficient toeffect ignition when contacted with the catalyst. Alternatively, thefeed can be ignited with an ignition source, such as a spark or flame.Once ignited, the process runs autothermally such that the exothermicheat of combustion drives the dehydrogenation/cracking process. Whilerunning autothermally, the paraffin feed does not have to be preheated,although it can be preheated if desired. Typical preheat temperaturesrange from about 40° C. to about 400° C.

[0042] As a general rule, the autothermal process operates at close tothe adiabatic temperature that is, essentially without loss of heat),which is typically greater than about 750° C., and preferably, greaterthan about 925° C. Typically, the autothermal process operates at atemperature less than about 1,150° C., and preferably, less than about1,050° C. Pressures range typically from about 1 atmosphere absolute(atm abs) (100 kPa abs) to about 20 atm abs (2,000 kPa abs), preferably,from about 1 atm abs (100 kPa abs) to about 10 atm (1,000 kPa abs), andmore preferably, from about 1 atm abs (1,000 kPa abs) to about 7 atm abs(700 kPa abs).

[0043] It is beneficial to maintain a high space velocity through thereaction zone, otherwise the selectivity to olefinic products maydecrease due to undesirable side reactions. Generally, the gas hourlyspace velocity (GHSV), calculated as the total flow of the hydrocarbon,oxygen, optional hydrogen, and optional diluent flows, is greater thanabout 50,000 ml total feed per ml catalyst per hour (h⁻¹) measured atstandard temperature and pressure (0° C., 1 atm). Preferably, the GHSVis greater than about 80,000 h⁻¹, and more preferably, greater than100,000 h⁻¹. Generally, the gas hourly space velocity is less than about6,000,000 h⁻¹, preferably, less than about 4,000,000 h⁻¹, morepreferably, less than 3,000,000 h⁻¹, measured as the total flow atstandard temperature and pressure. Gas flows are typically monitored inunits of liters per minute at standard temperature and pressure (slpm).The conversion of gas flow from “slpm” units to gas hourly spacevelocity units (h⁻¹) is made as follows:${GHSVh}^{- 1} = \frac{{slpm} \times 1000\quad {{cm}^{3}/\min} \times 60\quad \min \text{/}h}{{cross} - {{sectional}\quad {area}\quad {of}\quad {catalyst}\quad ( {cm}^{2} ) \times {length}\quad ({cm})}}$

[0044] When a paraffinic hydrocarbon is contacted with oxygen underautothermal process conditions in the presence of the catalyst describedhereinabove, an olefin, preferably a mono-olefin, is produced. Ethane isconverted primarily to ethylene. Propane and butane are convertedprimarily to ethylene and propylene. Isobutane is converted primarily toisobutylene and propylene. Naphtha and other higher molecular weightparaffins are converted primarily to ethylene and propylene.

[0045] The conversion of paraffinic hydrocarbon in the process of thisinvention can vary depending upon the specific feed composition,catalyst, and process conditions employed. For the purposes of thisinvention, “conversion” is defined as the mole percentage of paraffinichydrocarbon in the feed which is converted to products. Generally, atconstant pressure and space velocity, the conversion increases withincreasing temperature. Typically, at constant temperature and pressure,the conversion does not change significantly over a wide range of highspace velocities employed. In this process, the conversion of paraffinichydrocarbon is typically greater than about 45 mole percent, preferably,greater than about 55 mole percent, and more preferably, greater thanabout 60 mole percent.

[0046] Likewise, the selectivity to products will vary depending uponthe specific feed composition, catalyst, and process conditionsemployed. For the purposes of this invention, “selectivity” is definedas the percentage of carbon atoms in the converted paraffin feed whichreact to form a specific product. For example, the olefin selectivity iscalculated as follows:

[0047] Generally, the olefin selectivity increases with increasingtemperature up to a maximum value and declines as the temperaturecontinues to rise. Usually, the olefin selectivity does not changesubstantially over a wide range of high space velocities employed. Inthe process of this invention, the olefin selectivity, preferably, thecombined selectivity to ethylene and propylene, is typically greaterthan about 60 carbon atom percent, preferably, greater than about 70carbon atom percent, and more preferably, greater than about 80 carbonatom percent. Other products formed in smaller quantities includemethane, carbon monoxide, carbon dioxide, propane, butenes, butadiene,propadiene, acetylene, methylacetylene, and C₆₊ hydrocarbons. Acetylenecan be hydrogenated downstream to increase the overall selectivity toolefin. Carbon monoxide, carbon dioxide, and methane may be recycled, atleast in part, to the reactor.

[0048] Water is also formed in the process of this invention from thecombustion of hydrogen or hydrocarbon. Preferably, water is formed bythe combustion of hydrogen. Accordingly, it is advantageous to recyclethe hydrogen in the product stream, obtained from the oxidativedehydrogenation of the paraffinic hydrocarbon, back to the reactor. Thepresence of hydrogen in the feed minimizes the formation of carbonoxides by reacting with the oxygen to produce water and energy.Optimally, the hydrogen needed to meet the demands of the processessentially equals the hydrogen formed during conversion of theparaffinic hydrocarbon to olefin. Under these balanced conditions, thehydrogen forms a closed loop wherein there is essentially no demand foradditional hydrogen to be added to the fuel.

[0049] Over time the catalyst may lose activity due to the loss ofcatalytic components by vaporization. It has now been discovered thatthe catalyst can be easily regenerated on-line during the autothermaloxidation process. With this regeneration method, there is no need toshut down the process and remove the catalyst from the reactor. Rather,the regeneration comprises contacting the front face of the partiallydeactivated or fully deactivated catalyst with a Group 8B metal compoundand/or a promoter metal compound in situ during operation underautothermal process conditions. Typically, the front face of thecatalyst is contacted with a solution containing the Group 8B metalcompound and/or promoter metal compound. Details of the equipment andcontacting methods have been described hereinbefore for front faceon-line loading of the monolith.

[0050] The invention will be further clarified by a consideration of thefollowing examples, which are intended to be purely illustrative of theuse of the invention. Other embodiments of the invention will beapparent to those skilled in the art from a consideration of thisspecification or practice of the invention as disclosed herein. Unlessotherwise noted, all percentages are given on a mole percent basis.Selectivities are given on a carbon atom percent basis.

EXAMPLE 1 (E-1)-Autothermal Oxidation of Ethane to Ethylene over Pt-Snon Fiber Monolith

[0051] A catalyst comprising platinum and tin in a Pt:Sn atomic ratio1:7 on a fiber mat was prepared as follows. A non-woven fiber monolith(3M Corporation, Nextel® brand 312, non-woven pressed fiber mat; outerdimensions, 18 mm diameter by 2 mm thick; filament diameter, 10-12microns) was impregnated to incipient wetness with an aqueous solutionof hydrogen hexachloroplatinate (0.075 g in 7.5 ml water) and then airdried overnight. The dried monolith was calcined in air at 100° C. for 1h and then at 600° C. for 2 h. The platinum loading, determined bydifference in weights, was found to be 2 weight percent. The monolithwas further impregnated with an aqueous solution of stannous chloride(0.05 g in 7.5 ml water) containing 2 drops of hydrochloric acid toassist in the dissolution of the salt. Sufficient tin solution was usedto give a Pt:Sn atomic ratio of 1:7. After drying in air overnight, theimpregnated monolith was calcined in air at 100° C. for 1 h and at 700°C. for 2 h.

[0052] The catalyst was packed between blank alumina foam monoliths(outer diameter 18 mm by 10 mm length; 45 pores per linear inch) andinserted into a quartz reactor. A mixture of ethane, hydrogen, nitrogen,and oxygen was fed to the reactor. The gas mixture was heated indirectlyby holding a Bunsen burner flame to the outside of the reactor until thecatalyst lit off. Once the catalyst was ignited, the Bunsen burner wasremoved and the process was run autothermally. The reactor was radiallyinsulated to maintain adiabatic and autothermal operation. Pressure was1.34 atm abs. Autothermal temperature was typically between 800° C. and1,100° C. Process conditions and results are summarized in Table 1.TABLE 1 Autothermal Oxidation of Ethane to Ethylene^((a)) Catalyst: 2%Pt on Non-Woven Fiber Mat (Sn/Pt = 7:1) Total C₂H₆/ H₂/ Flow O₂ O₂ %Rate, Molar Molar % C₂H₆ % Selectivity: slpm Ratio Ratio N₂ Conv C₂H₄ COCO₂ CH₄ C₂H₂ C_(3,4) 5.0 2 0 30 69.2 69.8 14.7 6.9 4.6 0.5 3.5 7.5 2 220 68.2 84.0 5.5 0.5 5.7 0.2 4.1

[0053] It was seen that a catalyst comprising platinum and tin depositedon a ceramic fiber mat support was capable of oxidizing ethane toethylene in the presence of oxygen and hydrogen under autothermalconditions. Ethane conversion was between 68 and 69 percent; ethyleneselectivity reached a high of 84.0 percent. Carbon monoxide was lowestat 5.5 percent.

[0054] Comparative Experiment 1 (CE-1)—Autothermal Oxidation of Ethaneto Ethylene Over Pt-Sn on Foam Monolith

[0055] An alumina foam monolith (outer diameter 18 mm by 10 mm length;45 pores per linear inch) was impregnated to incipient wetness with anaqueous solution of hydrogen hexachloroplatinate (0.3 g in 2.5 ml water)and dried overnight under ambient conditions. The dried monolith wascalcined in air at 100° C. for 1 h and then at 600° C. for 2 h. Theplatinum loading was 2 weight percent. The monolith was furtherimpregnated with an aqueous solution of stannous chloride (1.8 g in 2.5ml water) acidified with 4 drops of hydrochloric acid to assist in thedissolution of the salt. After drying overnight, the monolith wascalcined in air at 100° C. for 1 h and at 700° C. for 2 h. The Sn:Ptatomic ratio was 7:1. The catalyst was packed into a quartz reactor asin E-1. A feed stream comprising ethane, hydrogen, nitrogen, and oxygenwas fed through the catalyst; the catalyst was ignited; and the processwas run autothermally in the manner described in E-1. Results are shownin Table 2. TABLE 2 Autothermal Oxidation of Ethane to Ethylene^((a))Catalyst: 2% Pt on Alumina Foam Monolith (Sn/Pt = 7:1) Total C₂H₆/ H₂/Flow O₂ O₂ % Rate, Molar Molar % C₂H₆ % Selectivity: slpm Ratio Ratio N₂Conv C₂H₄ CO CO₂ CH₄ C₂H₂ C_(3,4) 5.0 2 0 30 68.8 69.7 15.4 6.9 4.2 0.23.6 7.5 2 2 20 67.6 84.1 5.2 0.3 5.2 1.3 3.9

[0056] It was seen that a catalyst comprising platinum and tin on analumina foam monolith was capable of oxidizing ethane to ethylene in thepresence of hydrogen and oxygen under autothermal conditions. Ethaneconversion was between 68 and 69 percent; ethylene selectivity reached ahigh of 84.1 percent. When E-1 was compared with CE-1 under similarprocess conditions, it was seen that the process using the catalystprepared on a fiber monolith was comparable to the process with thecatalyst prepared on a foam monolith. Whereas the foam monolith is proneto fracture under long-term use, the fiber support advantageously is notprone to fracture.

[0057] Comparative Experiment 2 (CE-2)-Autothermal Oxidation of Ethaneto Ethylene Over Pt Gauze Coated with Tin

[0058] Three gauzes (Alfa Aesar) composed of pure platinum (99.9 weightpercent metals basis) woven from platinum wires (0.0762 mm wirediameter; 100 mesh (149 microns); 18 mm, external gauze diameter) werecoated on both sides with metallic tin to a thickness of 3000 Å by useof metal evaporation techniques. The three gauzes were packed togetherbetween two blank alumina foam monoliths (outer diameter 18 mm by 10 mmlength; 45 pores per linear inch), and inserted into a quartz reactor. Amixture of ethane, hydrogen, nitrogen, and oxygen was passed through thereactor; the catalyst was lit, and the process was run autothermally asdescribed in E-1 hereinabove. Process conditions and results are shownin Table 3. TABLE 3 Autothermal Oxidation of Ethane to Ethylene^((a))Catalyst: 100 Mesh Platinum Gauze (3000 Å Sn) Total C₂H₆/ H₂/ Flow O₂ O₂% Rate, Molar Molar % C₂H₆ % Selectivity: slpm Ratio Ratio N₂ Conv C₂H₄CO CO₂ CH₄ C₂H₂ C_(3,4) 7.5 2 2 20 62.2 81.1 6.6 0.4 4.5 3.3 4.1

[0059] It was seen that a catalyst comprising platinum gauze coated withtin was capable of oxidizing ethane to ethylene in the presence ofoxygen and hydrogen under autothermal conditions. Ethane conversion was62.2 percent; ethylene selectivity was 81.1 percent. Carbon monoxideselectivity was 6.6 percent. When E-1 was compared with CE-2 underidentical process conditions, it was seen that the catalyst prepared onthe fiber monolith achieved a higher conversion, a higher ethyleneselectivity, and a lower carbon monoxide selectivity than the catalystprepared on the gauze.

EXAMPLE 2 (E-2)-Catalyst Regeneration:On-line Sn Addition to Catalyst

[0060] A platinum-tin catalyst was prepared on a non-woven fiber matmonolith as described in E-1 hereinabove. The platinum loading was 2weight percent, and the Sn:Pt atomic ratio was 7:1. The catalyst waspacked between two blank foam alumina monoliths (outer diameter 18 mm by10 mm length; 45 pores per linear inch) in a quartz reactor. A mixtureof ethane, hydrogen, nitrogen, and oxygen was fed through the reactorunder the process conditions shown in Table 4. Light-off of the catalystand autothermal operation were as described in E-1 hereinabove. Theselectivity and conversion were monitored at 1.5 and 20 h of continuousoperation, as shown in Table 4. TABLE 4 On-Line Regeneration of Pt-SnCatalyst^((a)) Time Total C₂H_(6/) H₂/ on Flow O₂ O₂ line Rate, MolarMolar % % % Selectivity: h slpm Ratio Ratio N₂ ConvC₂H₆ C₂H₄ CO CO₂ CH₄C₂H₂ C_(3,4) 1.5 7.5 2 2 20 68.2 84.0 5.5 0.5 5.7 0.2 4.1 20.0  7.5 2 220 60.4 81.0 7.4 0.9 5.6 0.0 5.1 After 7.5 2 2 20 66.1 83.2 5.8 0.4 5.40.9 4.3 Regen.

[0061] It was found that the ethane conversion and ethylene selectivitydecreased with time. At 20 h of continuous use the partially deactivatedcatalyst was regenerated using the following on-line regenerationtechnique. Stannous chloride (0.1 g) was dissolved in distilled water (8ml) containing 1 drop of hydrochloric acid to assist solubility. Thissolution (0.4 ml) was dripped uniformly onto the front surface of thepartially deactivated catalyst while the apparatus was in use underautothermal conditions. The apparatus used for the on-line regenerationwas similar to that shown in FIG. 1. Results of the on-line regenerationare found in Table 4. It was found that the on-line addition of tin tothe partially deactivated catalyst regenerated the catalyst restoringboth ethane conversion and ethylene selectivity to near initial levels.

EXAMPLE 3 (E-3)-On-line Catalyst Preparation: Front Face Loading

[0062] Two blank alumina foam monoliths (outer diameter 18 mm by 10 mmlength; 45 pores per linear inch) were packed into a quartz reactor, anda mixture of ethane, hydrogen, nitrogen, and oxygen was passed throughthe reactor. The total feed flow rate was maintained at 7.5 slpm;nitrogen dilution was 20 percent; and the ethane/oxygen andhydrogen/oxygen molar ratios were both maintained at 2/1. The monolithswere heated using a Bunsen burner flame, but they failed to light off.Hydrogen hexachloroplatinate (0.04 g) was dissolved in distilled water(5 ml). A portion of this solution was sucked into a syringe (1 cc), andthe solution (0.4 ml) was uniformly dripped onto the front surface ofthe front alumina monolith under ignition conditions (external heat fromBunsen burner). The apparatus for delivering the solution was similar tothat shown in FIG. 1. The solution was observed to dry quickly under theinfluence of external heating and changed color from yellow to black,before the catalyst lit off. Results using this front face loadedcatalyst, which was prepared on-line, are given in Table 5 (first row).TABLE 5 On-Line Catalyst Preparation^((a)) Total C₂H₆/ H₂/ Flow O₂ O₂ %Rate, Molar Molar % C₂H₆ % Selectivity: Catalyst slpm Ratio Ratio N₂Conv C₂H₄ CO CO₂ CH₄ C₂H₂ C_(3,4) Pt 7.5 2 2 20 60.5 81.1 9.1 0.5 4.50.4 4.4 Pt—Sn 7.5 2 2 20 65.2 84.4 5.2 0.3 5.0 1.2 3.9 Pt—Sn—Cu 7.5 2 220 64.3 84.6 5.6 0.6 4.7 0.9 3.6

[0063] After the platinum solution was dripped onto the blank monolithand lit off, the syringe was replaced by a second syringe containing anaqueous solution of tin chloride (0.15 g in 5 ml distilled water).Approximately 0.4 ml of this solution was dripped uniformly underautothermal conditions over the front face of the platinum catalyst toprepare a platinum-tin catalyst in situ. Results using this catalyst areshown in Table 5 (second row). It was found that the on-line addition oftin to the front face of platinum catalyst produced a Pt-Sn catalystwith improved ethane conversion and improved ethylene selectivity. Also,carbon monoxide and carbon dioxide production were significantlyreduced. Thereafter, the syringe was replaced by a third syringecontaining an aqueous solution of copper nitrate (0.15 g in 5 mldistilled water). Approximately 0.4 ml of this solution was drippeduniformly over the front face of the platinum-tin catalyst underautothermal conditions to prepare a platinum-tin-copper catalyst insitu. Results are shown in Table 5 (third row). It was found that theon-line addition of copper to the front face of the platinum-tincatalyst produced a Pt—Sn—Cu catalyst which improved performance whencompared with the pure platinum catalyst.

[0064] Comparative Experiment 3 (CE-3)-Uniform Catalyst Loading

[0065] An alumina monolith (outer diameter 18 mm by 100 mm length; 45pores per linear inch) was uniformly loaded by impregnation to incipientwetness with an aqueous solution (2 ml) of hydrogen hexachloroplatinateand then dried overnight under ambient conditions. The dried monolithwas calcined in air at 100° C. for 1 h and then at 600° C. for 2 h. Theplatinum loading was 5 weight percent. The platinum catalyst was packedbetween blank alumina monoliths and inserted into the center of a quartzreactor, in a manner similar to E-1 hereinabove. A mixture of ethane,hydrogen, nitrogen, and oxygen was passed through the reactor andignited as in Example 1. After light off, the process was runautothermally as in Example 1, with the process conditions and resultsshown in Table 6. TABLE 6 Ethane Oxidation to Ethylene^((a)) Catalyst:5% Pt on Alumina Foam Monolith Total C₂H₆/ H₂/ Flow O₂ O₂ % Rate, MolarMolar % C₂H₆ % Selectivity: slpm Ratio Ratio N₂ Conv C₂H₄ CO CO₂ CH₄C₂H₂ C_(3,4) 5.0 2 0 30 62.5 61.5 23.8 6.6 3.5 0.2 4.4 7.5 2 2 20 63.974.6 12.8 0.9 6.0 0.3 5.4

[0066] When CE-3 (Table 6, second row) was compared with E-3 underidentical process conditions (Table 5, first row), it was found that theplatinum catalyst which was loaded on-line onto the front face of themonolith advantageously achieved a higher ethylene selectivity and lowercarbon monoxide and carbon dioxide selectivities, as compared with thecomparative platinum catalyst which was uniformly loaded.

What is claimed is:
 1. A process of preparing an olefin comprisingcontacting a paraffinic hydrocarbon with oxygen in the presence of acatalyst, the contacting being conducted under autothermal processconditions sufficient to prepare the olefin, the catalyst comprising atleast one Group 8B metal and, optionally, at least one promoter metal,said metal(s) being supported on a fiber monolith support.
 2. Theprocess of claim 1 wherein the paraffinic hydrocarbon comprises one ormore saturated hydrocarbons each having from 2 to about 25 carbon atoms.3. The process of claim 2 wherein the paraffinic hydrocarbon comprisesethane, propane, or mixtures thereof.
 4. The process of claim 2 whereinthe paraffinic hydrocarbon is selected from naphtha, natural gascondensates, gas oils, vacuum gas oils, and mixtures thereof.
 5. Theprocess of claim 1 wherein the molar ratio of paraffinic hydrocarbon tooxygen ranges from about 3 to about 13 times the stoichiometric ratio ofhydrocarbon to oxygen for complete combustion to carbon dioxide andwater.
 6. The process of claim 1 wherein the molar ratio of paraffinichydrocarbon to oxygen is greater than about 0.1:1 and less than about3.0:1.
 7. The process of claim 1 wherein a diluent is used.
 8. Theprocess of claim 7 wherein the diluent is used in an amount greater thanabout 0.1 mole percent and less than about 70 mole percent, based on thetotal reactant feed.
 9. The process of claim 1 wherein the Group 8Bmetal is a platinum group metal.
 10. The process of claim 9 wherein theplatinum group metal is platinum.
 11. The process of claim 1 wherein thesupport is a ceramic selected from silica, alumina, silica-aluminas,aluminosilicates, zirconia, titania, boria, zirconia mullite alumina,lithium aluminum silicates, and oxide-bonded silicon carbide.
 12. Theprocess of claim 11 wherein the ceramic support comprises from about 60to about 100 weight percent alumina.
 13. The process of claim 1 whereineach fiber comprising the fiber monolith has a diameter greater thanabout 1 micron and less than about 20 microns, and a surface areagreater than about 0.001 m²/g and less than about 1 m²/g.
 14. Theprocess of claim 1 wherein the fiber monolith is in the form of a fibermat.
 15. The process of claim 1 wherein the promoter metal is selectedfrom Groups 2A, 1B, 3A, 4A, and the rare earth lanthanide elements, andmixtures thereof.
 16. The process of claim 15 wherein the atomic ratioof Group 8B metal to promoter metal ranges from greater than about 1:10to less than about 1:0.5.
 17. The process of claim 1 wherein thetemperature is greater than about 750° C. and less than about 1,150° C.18. The process of claim 1 wherein the pressure ranges from about 1 atmabs (100 kPa abs) to about 20 atm abs (2,000 kPa abs).
 19. The processof claim 1 wherein the gas hourly space velocity is greater than about80,000 h⁻¹ and less than about 6,000,000 h⁻¹.
 20. The process of claim 1wherein the conversion of paraffinic hydrocarbon is greater than about55 mole percent.
 21. The process of claim 1 wherein the olefinselectivity is greater than about 70 carbon atom percent.
 22. Theprocess of claim 1 wherein the paraffin is ethane and the contacting isconducted under autothermal conditions at an ethane to oxygen molarratio greater than about 1.5:1 and less than about 2.7:1, a gas hourlyspace velocity greater than about 100,000 h⁻¹ and less than about4,000,000 h⁻¹, wherein a diluent is used in an amount greater than about1 mole percent and less than about 70 mole percent based on the totalreactant feed, wherein the Group 8B metal is platinum, and the fibermonolith comprises from about 60 to about 100 weight percent alumina.23. A catalyst composition comprising at least one Group 8B metal and atleast one promoter metal, said metals being supported on a fibermonolith support.
 24. The composition of claim 23 wherein the Group 8Bmetal is a platinum group metal.
 25. The composition of claim 24 whereinthe platinum group metal is platinum.
 26. The composition of claim 23wherein the promoter metal is selected from Groups 2A, 1B, 3A, 4A, andthe lanthanide elements, and mixtures thereof.
 27. The composition ofclaim 23 wherein the monolith is a ceramic selected from silica,alumina, silica-aluminas, aluminosilicates, zirconia, titania, boria,zirconia mullite alumina, lithium aluminum silicates, and oxide-bondedsilicon carbide.
 28. The composition of claim 27 wherein the ceramicmonolith comprises from about 60 to about 100 weight percent alumina.29. The composition of claim 23 wherein each of the fibers comprisingthe fiber monolith has a fiber diameter greater than about 1 micron andless than about 20 microns, and a surface area greater than about 0.001m²/g and less than about 1 m²/g.
 30. The composition of claim 23 whereinthe fiber monolith consists essentially of 62 weight percent alumina, 24weight percent silica, and 14 weight percent boria.
 31. A catalystcomposition comprising at least one Group 8B metal and, optionally, atleast one promoter metal, said metal(s) being supported on the frontface of a monolith support.
 32. The composition of claim 31 wherein theGroup 8B metal is a platinum group metal.
 33. The composition of claim32 wherein the platinum group metal is platinum.
 34. The composition ofclaim 31 wherein the promoter metal is selected from Groups 2A, 1B, 3A,4A, and the lanthanide elements, and mixtures thereof.
 35. Thecomposition of claim 31 wherein the monolith is a ceramic selected fromsilica, alumina, silica-aluminas, aluminosilicates, zirconia, titania,boria, zirconia mullite alumina, lithium aluminum silicates, andoxide-bonded silicon carbide.
 36. The composition of claim 31 whereinthe ceramic monolith comprises from about 60 to about 100 weight percentalumina.
 37. The composition of claim 31 wherein the monolith support isin the form of a honeycomb, foam, or fiber mat.
 38. A process ofpreparing an olefin comprising contacting a paraffinic hydrocarbon withoxygen in the presence of a catalyst, the contacting being conductedunder autothermal process conditions sufficient to prepare the olefin,the catalyst comprising at least one Group 8B metal and, optionally, atleast one promoter metal, said metal(s) being supported on the frontface of a monolith support.
 39. The process of claim 38 wherein theparaffinic hydrocarbon comprises one or more saturated hydrocarbons eachhaving from 2 to about 25 carbon atoms.
 40. The process of claim 38wherein the paraffinic hydrocarbon comprises ethane, propane, ormixtures thereof.
 41. The process of claim 38 wherein the paraffinichydrocarbon is selected from naphtha, natural gas condensates, gas oils,vacuum gas oils, and mixtures thereof.
 42. The process of claim 38wherein the molar ratio of paraffinic hydrocarbon to oxygen ranges fromabout 3 to about 13 times the stoichiometric ratio of hydrocarbon tooxygen for complete combustion to carbon dioxide and water.
 43. Theprocess of claim 38 wherein the molar ratio of paraffinic hydrocarbon tooxygen is greater than about 0.1:1 and less than about 3.0:1.
 44. Theprocess of claim 38 wherein a diluent is used.
 45. The process of claim44 wherein the diluent is used in an amount greater than about 0.1 molepercent and less than about 70 mole percent, based on the total reactantfeed.
 46. The process of claim 38 wherein the Group 8B metal is aplatinum group metal.
 47. The process of claim 46 wherein the platinumgroup metal is platinum.
 48. The process of claim 38 wherein the supportis a ceramic selected from silica, alumina, silica-aluminas,aluminosilicates, zirconia, titania, boria, zirconia mullite alumina,lithium aluminum silicates, and oxide-bonded silicon carbide.
 49. Theprocess of claim 48 wherein the ceramic support comprises from about 60to about 100 weight percent alumina.
 50. The process of claim 38 whereinthe promoter metal is selected from Groups 2A, 1B, 3A, 4A, and the rareearth lanthanide elements, and mixtures thereof.
 51. The process ofclaim 38 wherein the atomic ratio of Group 8B metal to promoter metalranges from greater than about 1:10 to less than about 1:0.5.
 52. Theprocess of claim 38 wherein the temperature is greater than about 750°C. and less than about 1,150° C.
 53. The process of claim 38 wherein thepressure ranges from about 1 atm abs (100 kPa abs) to about 20 atm abs(2,000 kPa abs).
 54. The process of claim 38 wherein the gas hourlyspace velocity is greater than about 80,000 h⁻¹ and less than about6,000,000 h⁻¹.
 55. The process of claim 38 wherein the conversion ofparaffinic hydrocarbon is greater than about 55 mole percent.
 56. Theprocess of claim 38 wherein the olefin selectivity is greater than about70 carbon atom percent.
 57. The process of claim 38 wherein the paraffinis ethane and the contacting is conducted under autothermal conditionsat an ethane to oxygen molar ratio greater than about 1.5:1 and lessthan about 2.7:1, a gas hourly space velocity greater than about 100,000h⁻¹ and less than about 4,000,000 h⁻¹, wherein a diluent is used in anamount greater than about 1 mole percent and less than about 70 molepercent based on the total reactant feed, wherein the Group 8B metal isplatinum, and the monolith comprises from about 60 to about 100 weightpercent alumina.